Image quality in any imaging system can often be limited by noise including speckle noise in coherent illumination, or by lower resolution or a lack of contrast due to scattered light or light from secondary light sources.
For more than four decades, confocal scanning laser microscopy has been used successfully to analyze samples in many diverse fields, ranging from biology1 to the characterization of materials2. One type of scanning laser microscope with a large field of view is known as a Macroscope. This is an example of an instrument in which, for 1 scan direction, the sample is scanned relative to the beam. Webb and co-workers3 presented the confocal scanning laser ophthalmoscope for viewing the ocular fundus, using the ocular optics as a microscope objective. Optical coherence tomography is also used generally to analyze samples and to image the ocular fundus. Images can be in 2 dimensions perpendicular to the optical beam incident on the sample, in a section with 1 dimension along the incident beam or in line scans in either of these two sections, and each of these modalities can be used to build up a 3 dimensional image of the object or the eye in depth. Since the optics of the eye degrade the image, additional improvements have been made to fundus imaging, such as adaptative optics4, deconvolution techniques5 or changes in the beam diameter and its entry position in the pupil of the eye6. The methodology outlined here can also be combined with a microscope (without beam scanning) with either confocal or non-confocal imaging.
The polarization properties of light have been used in conjunction with imaging techniques in target detection7, optical coherence tomography8,9, ophthalmologic diagnosis10, remote sensing11 and microscopy12. In general, optical imaging with polarization has been reported to improve contrast, reduce noise and provide useful information about scenes (not available with polarization-blind imaging). Structural information (for example nerve fiber layer thickness10) obtained from the polarization properties is also useful.
Confocal scanning laser ophthalmoscopy, scanning laser ophthalmoscopy and ocular optical coherence tomography are used for the diagnosis of eye diseases and disorders that affect structures at the rear of the eye and for basic scientific and biomedical investigations of these structures. Confocal scanning laser microscopy is used to characterize many materials and for biomedical investigations, including the diagnosis of disorders and diseases of the cornea of the eye. Major limitations to the recognition of features limit diagnosis and evaluation of structures viewed in confocal scanning laser ophthalmoscopy, in confocal scanning laser microscopy and in optical coherence tomography. These limitations include pixel to pixel noise, lowered contrast and a lack of resolution. A lowering of contrast and an increase in the size of the features resolved is partly due to the imperfect optical quality of the objective that in the case of ophthalmoscopy and ocular optical coherence tomography is the eye itself. Noise can be increased due to imperfect optics or due to a lower signal reflected from the structures being observed, reducing the signal to noise ratio. However, these reductions in contrast, resolution and signal to noise ratio are a function of the polarization properties of the features being imaged.
Therefore, it would be very advantageous to provide a method which provides improved image contrast, image resolution and/or the signal to noise ratio of a given image.